---decode
$input = “vikivikivikivikivikivyapvyapvyapvyapvyapnandnandnandnandnandviki”
$output = [System.Text.Encoding]::Unicode.GetString([System.Convert]::FromBase64String($input))
$output

--encode
$input = ‘text to be encoded’
$By = [System.Text.Encoding]::Unicode.GetBytes($input)
$output =[Convert]::ToBase64String($By)
$output